struct ipc_perm and size of seq member

[Geoff Keating]

> Date: Fri, 22 Sep 2000 14:18:37 +0200
> From: Franz Sirl <Franz.Sirl-kernel@lauterbach.com>
> 
> Hi,
> 
> I'm finally able to run 2.4.0-t8 on my B&W G3 and can now track down the 
> remaining problems with glibc-2.1.9x. With 2.4 I still have an IPC problem, 
> that maybe related to different notion of the size of seq. 2.4 on PPC 
> defines it as 'unsigned long', but glibc-2.1.94 uses it as 'unsigned 
> short'. Besides the missing padding in powerpc/bits/ipc.h, why does glibc 
> use a 16bit type here, while the kernel uses 32bit? Is this required for 
> userspace compatibility?

This structure used to be

struct ipc_perm
{
	__kernel_key_t	key;
	__kernel_uid_t	uid;
	__kernel_gid_t	gid;
	__kernel_uid_t	cuid;
	__kernel_gid_t	cgid;
	__kernel_mode_t	mode; 
	unsigned short	seq;
};

so the kernel change breaks backward compatibility, and the glibc
problem you're seeing is just one aspect of this.

Note that this structure has padding _after_ 'seq', not before.
'mode' is 4-byte aligned, being an int.

-- 
- Geoffrey Keating <geoffk@cygnus.com>